The production of commercial animals for human food by abatoirs is one of the worlds largest industries. Less than one-half of the live weight of the commercial animals are consumed by humans with the remainder left for disposal. Many of the abatoir by-products and wastes still contain potentially valuable materials, but at present are either discharged into water or onto land. This can cause unsightly landscapes, health hazards, malodorous atmospheres, and pollution of land and water.
Progress has been significant in the recovery of proteinaceous animal wastes and by-products, and in their utilization as pet food, animal feed, protein, supplements, and nitrogen fertilizers. In my U.S. Pat. No. 5,021,077, a method is provided for the preparation of natural nitrogenous granules. However, there has been little progress provided in the area of recovery of fats as granular products which may be used effectively as supplements for commercial animal feeds.
Fats are one of the most important ingredients in commercial animal by-products, and are usually the largest constituent in the sludges collected from abatoir waste water treatment operations. These fats represent large potential values if there were efficient methods available for their recovery in useful forms. Unfortunately, at the present time, fat constitutes a serious sensory and pollution problem because it is not usefully recovered, but rapidly putrefies, creating malodors and supporting growth of pathogens which cause health hazards.
At the present time, rendering by boiling or steaming is the prime method used if fats are recovered from abatoir operations. Rendering is unable to provide free-flowing, high integrity particulate fats free of malodors and pathogens. Rendering, by definition, melts the fats into a liquid, but in actual practice, usually produces a soft malodorous semisolid which is difficult to handle, blend, or use.
To maintain clean and sanitary conditions in abatoir operating areas, the areas are washed with water frequently, or continuously. The wash water is usually quickly, or continuously, removed from the operating area and sent to an effluent water treatment plant. There the insoluble solids are separated as sludges from the effluent water. These aqueous sludges, including those which float and those which settle in water, usually contain between 5 and 50 percent fat on a dry basis, and are typical of the fats now wasted which cause pollution problems. Although the sludge generation techniques vary somewhat, depending on the individual operations and the type animals being produced, the aqueous sludges which contain fat are essentially the same.
High fat abatoir sludges are usually generated in slaughterhouses; however, mortality frequently occurs in commercially produced animals in areas outside those desired. For example, as animals, particularly poultry, are grown and maintained, an inevitable mortality rate occurs. This rate amounts to between 5 and 7 percent of the poultry raised, for many and varied causes. Disposal of these animals has been to date a very difficult task which created hazards of disease spread to other animals, and which could cause damage to various parts of the environment.
A recently developed method for handling this animal mortality problem, comminutes these animals into a fluid which is pumped into a treatment tank where it is maintained at a low pH, usually created by microbial action, to pickle the solids, prevent putrefaction, and to provide a stabilized abatoir sludge for subsequent periodic collection and disposal. These aqueous pickled sludges typically contain 30 to 50 percent dry matter which comprises between 10 and 40 percent fat. The art has provided no method for recovering fat values from those abatoir sludges as malodor and pathogen free animal feed supplement particles.
Another abatoir sludge source of fats is the residue from hatching eggs. This sludge may be recovered by washing and water treatment or by simple mechanical collection, and may comprise egg mortality, egg residue after hatching, and chick mortality. The sludges from hatcheries typically contain between 40 and 60 percent dry matter comprising about 10 to 30 percent fat on an as is basis. No satisfactory method for recovery of the fats contained in this abatoir sludge as malodor and pathogen free animal feed supplement particles has been provided by the art.
Composting has been used for the disposal of some of the animal by-products, but its effectiveness with high fat wastes, such as the abatoir sludges, has been limited. While composting usually slowly rids the area of malodors, it dilutes the by-products, increases the volume to be eventually disposed of into the environment, and eliminates any values of fat which might have been recovered as an animal feed supplement.
Typical composting technique is described by W. S. Galler and C. B. Davey in their paper entitled "High Rate of Poultry Manure Composting With Sawdust", published in the Proceedings, International Symposium On Livestock Wastes, Apr. 19-22, 1971, Columbus, Ohio.
A review of the literature provides no method for recovering particulate animal feed fats free of malodors and pathogens from abatoir sludges.